So far white LEDs were realized by combining a blue-emitting diode with a yellow emitting phosphor. Such a combination has a poor color rendition, which, however, can be improved significantly by using a red-green-blue system (RGB). Such a system uses for example a red and blue emitter in combination with a green-emitting aluminate phosphor, like SrAl2O4:Eu or BaAl2O4:Eu, with the possible addition of Mn to Eu, whose emission maximum is around 520 nm, see U.S. Pat. No. 6,278,135. However, the position of the excitation and emission bands of theses aluminates is not optimum. They have to be excited by short UV in the range of 330 to 400 nm.
On the other hand, some phosphors derived from the class of MSiON are known; see e.g. “On new rare-earth doped M—Si—Al—O—N materials” by van Krevel, TU Eindhoven 2000, ISBN 90-386-2711-4, Chapter 6. They are doped with Tb. Emission is achieved upon excitation by 365 nm or 254 nm.